Flight Dynamics Investigation of Compound Helicopter Configurations

Abstract

Compounding has often been proposed as a method to increase the maximum speed of the helicopter. There are two common types of compounding known as wing and thrust compounding. Wing compounding offloads the rotor at high speeds delaying the onset of retreating blade stall, hence increasing the maximum achieveable speed, whereas with thrust compounding, axial thrust provides additional propulsive force. The concept of compounding is not new but recently there has been a resurgence of interest in the configuration due to the emergence of new requirements for speeds greater than those of conventional helicopters. The aim of this paper is to investigate the dynamic stability characteristics of compound helicopters and compare the results with a conventional helicopter. The paper discusses the modelling of two compound helicopters, with the first model featuring a coaxial rotor and pusher propeller. This configuration is known as the coaxial compound helicopter. The second model, known as the hybrid compound helicopter, features a wing and two propellers providing thrust compounding. Their respective trim results are presented and contrasted with a baseline model. Furthermore, using a numerical differentiation technique, the compound models are linearised and their dynamic stability assessed. The results show that the frequency of the coaxial compound helicopter's dutch roll mode is less than that of the baseline helicopter and there is also greater roll damping. With regards to the hybrid compound helicopter the results show greater heave damping and the stabilisation of the phugoid due to the addition of the wing and propellers. stability and control matrices C q , C t torque and thrust coefficient C t u , C t l upper and lower rotor thrust coefficientnumber of rotor blades N p yawing moment due to roll rate (1/s) P coaxial rotor power (HP) R, R prop radius of the main rotor and propeller blade (m) U e forward speed at trim (m/s)

A Trimming Methodology for a New Coaxial Rotor Configuration of Robotic Helicopter Based on Rotor's Thrust Ratio

“…These situation also happened in conventional helicopter. Furthermore, the distribution trend of natural modes of dynamic model coincides well with the existed results [26].…”

Performance comparison between a conventional helicopter and compound helicopter configurations

“…This is perhaps due to the rudimentary nature of the coaxial inflow model which does not take into account the radial contraction of the upper rotor wake. However, the coaxial rotor model has shown to agree well [19] with the coaxial hover results provided by Harrington [40] and forward flight results by Dingeldein [41].…”

“…dynamics investigation of compound helicopters by Ferguson and Thomson [19], the comparison of a coaxial rotor to that of a single rotor gives similar power predictions. This is perhaps due to the rudimentary nature of the coaxial inflow model which does not take into account the radial contraction of the upper rotor wake.…”

“…This current study is a continuation of the compound helicopter work which focussed on the dynamic stability of these compound helicopter configurations [19]. The compound helicopter models are developed using the Helicopter Generic Simulation (HGS) model [17; 20].…”

Multilayer hierarchical control for robotic coax-helicopter based on the H∞ robustness and mixing control scheme

“…8 Moreover, the dynamic stability characteristics of the coaxial compound helicopter were taken into account and compared with a traditional helicopter in detail. 9 However, only few researches considered the complete model foundation and control design of a robotic coaxial rotor helicopter. 3 In addition, a coaxial helicopter is nonlinear uncertainty and severely coupling plant.…”